1. Field of the Invention
The invention is directed to a touch sensing structure and more particularly, to an optical touch sensing structure.
2. Description of Related Art
A conventional optical touch sensing structure is composed of a light-colored paper substrate and a plurality of black-ink patterns printed on the light-colored paper substrate. When an infrared emitted by an optical stylus passes through the optical touch sensing structure, the light-colored paper substrate directly reflects or scatters the infrared. The reflected or scattered infrared is also detected by an infrared camera disposed in the optical stylus. When the optical stylus contacts the optical touch sensing structure and moves on the surface of the optical touch sensing structure, a processor determines a position and a movement of a touched point according to the infrared intensity and image change sensed by the infrared camera.
Due to the rough surface of the light-colored paper substrate, the infrared generated by the optical stylus may be reflected and scattered toward a plurality of directions. As such, the infrared camera would capture a reflected image easily. That is to say, the optical stylus may still read a positional signal of a touched point even at a quite large tilting angle. However, the light-colored paper substrate itself is non-transparent, i.e. does not have enough light transmittance, and thus, a portion of light is shielded. Therefore, such type of optical touch sensing structure can not be applied to common displays. Moreover, the light-colored paper substrate reflects and scatters not only the infrared but also light emitted by a display and ambient light from the external, such that the image gets foggy, which leads to reduced contrast and sharpness of the image.